The separation of enantiomers and diastereoisomers (chiral separations) is a growing concern to modern chemists. Enantiomers of racemic drugs and agricultural chemicals, for example, frequently exhibit different degrees of activity and toxicity in biological systems, even though they differ from one another by only a rotational configuration of the molecule. Isolation of the individual enantiomers allows the specific properties of each to be determined.
Chiral separations are one of the most challenging types of purifications because of the extreme similarity between the two components in the racemic mixture; each is merely a mirror image of the other. Others have used chiral liquid chromatographic separations employing either a CSP or a CMPA as the chiral discriminating agent.
Using both a CSP and a CMPA is less frequent, but a publication by M. Fujita, et. al., "Highly Efficient Chromatographic Resolution of [Co(en).sub.3 ].sup.3+ Ion with a Column of TA(ES)Sephadex Containing D-Tartrate Groups", Chem. Lett., Chem. Soc. Japan (1975) pp. 473-474, described an improvement in the separation of Cobalt(III) complexes by using sodium L-tartrate as a CMPA in columns packed with partially esterified D-tartrate-Sephadex. One would expect these columns to be relatively unstable because of the likelihood that the ester functionality would hydrolyze and transesterify. In a related study, Pettersson and Gioeli, J. Chrom. 435 (1988) 225, used quinine as a CMPA to improve separation on an alkylquinidine-silica CSP. Quinine is not an actual enantiomer or diastereomer of the alkylquinidine, but appears to behave similarly. The poor predictability of analyte elution order with different mobile-phase additives may have resulted from this lack of true enantiomeric relationship between the additive and the CSP.